U.S. patent application number 12/293831 was filed with the patent office on 2010-09-09 for variable valve timing system and method for controlling the same.
This patent application is currently assigned to Toyota Jidosha Kabushiki Kaisha. Invention is credited to Tsukasa Abe, Kazuhiro Ichimoto, Makoto Yamazaki.
Application Number | 20100224153 12/293831 |
Document ID | / |
Family ID | 39047830 |
Filed Date | 2010-09-09 |
United States Patent
Application |
20100224153 |
Kind Code |
A1 |
Ichimoto; Kazuhiro ; et
al. |
September 9, 2010 |
VARIABLE VALVE TIMING SYSTEM AND METHOD FOR CONTROLLING THE
SAME
Abstract
A variable valve timing system changes a valve phase by reducing
an operation amount of an actuator at a speed reduction ratio that
varies depending on a phase region. When the valve phase is outside
a region in which the ratio of the amount of change in the phase
with respect to the operation amount of the actuator is low, namely
a high speed reduction ratio, the actuator may be operated due to,
for example, a reaction force applied to a camshaft, and an
undesirable valve phase change may result. Accordingly, when an
engine stop command is possibly issued, the target phase value is
restricted to a region more delayed than a phase restriction value
set in consideration of the amount by which the valve timing can be
changed from when an engine stop command is issued until when the
engine is stopped.
Inventors: |
Ichimoto; Kazuhiro;
(Nishikamo-gun, JP) ; Yamazaki; Makoto;
(Gotenba-shi, JP) ; Abe; Tsukasa; (Gotenba-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Toyota Jidosha Kabushiki
Kaisha
Toyota-shi
JP
|
Family ID: |
39047830 |
Appl. No.: |
12/293831 |
Filed: |
August 29, 2007 |
PCT Filed: |
August 29, 2007 |
PCT NO: |
PCT/IB07/02480 |
371 Date: |
September 22, 2008 |
Current U.S.
Class: |
123/90.17 |
Current CPC
Class: |
F02D 13/0265 20130101;
F02D 13/0203 20130101; F02D 2041/001 20130101; Y02T 10/18 20130101;
F02D 41/062 20130101; F02D 41/042 20130101; F01L 1/34 20130101;
Y02T 10/12 20130101 |
Class at
Publication: |
123/90.17 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2006 |
JP |
2006-232355 |
Claims
1. A variable valve timing system that changes opening/closing
timing of at least one of an intake valve and an exhaust valve
provided in an engine, comprising: a changing mechanism that
changes the opening/closing timing by changing a rotational phase
difference between a camshaft, which drives the valve of which the
opening/closing timing is changed, and a crankshaft by an amount of
change corresponding to an operation amount of an actuator, when
the engine is operating, wherein the changing mechanism sets a
ratio of the amount of change in the opening/closing timing with
respect to the operation amount of the actuator to a lower value
when the opening/closing timing is within a first phase region than
when the opening/closing timing is within a second phase region; a
target phase setting unit that sets target opening/closing timing
of at least one of the intake valve and the exhaust valve based on
an operating state of the engine; a phase control unit that sets
the operation amount of the actuator based on a result of
comparison between the target opening/closing timing and the actual
opening/closing timing; and a target phase restriction unit that
restricts the target opening/closing timing used when the engine is
operating such that the opening/closing timing is within the first
phase region when the engine is stopped due to the operation of the
actuator after a command to stop the engine is issued.
2. The variable valve timing system according to claim 1, wherein
the target phase restriction unit restricts the target
opening/closing timing to the first phase region when the engine is
being started.
3. The variable valve timing system according to claim 1, wherein
the target phase restriction unit restricts the target
opening/closing timing to a restriction range that includes the
first phase region and a phase region that has a phase difference
of equal to or smaller than a given amount with the first phase
region, when a vehicle is not running.
4. The variable valve timing system according to claim 3, further
comprising: a variable restriction range setting unit that sets the
given amount that defines the restriction range to which the target
opening/closing timing is restricted by the target phase
restriction unit based on a temperature of the engine.
5. The variable valve timing system according to claim 4, wherein
the variable restriction range setting unit sets the given amount
to a relatively small value when the temperature of the engine is
low.
6. The variable valve timing system according to claim 1, wherein
the first phase region includes a most delayed phase and a most
advanced-side phase of the first phase region is more delayed than
a predetermined phase, and the target phase setting unit sets the
target opening/closing timing to the opening/closing timing at the
most delayed phase after the command to stop the engine is
issued.
7. The variable valve timing system according to claim 1, wherein
the actuator is formed of an electric motor, and the operation
amount of the actuator corresponds to a rotational speed of the
electric motor relative to a rotational speed of the camshaft.
8. The variable valve timing system according to claim 1, wherein
the operating state of the engine includes an engine speed and an
intake air amount.
9. The variable valve timing system according to claim 8, wherein
the target phase setting unit sets the target opening/closing
timing based on the engine speed and the intake air amount when the
engine is operating under load conditions.
10. The variable valve timing system according to claim 8, wherein
the target phase setting unit sets the target opening/closing
timing based on the engine speed when the engine is operating under
no-load conditions.
11. The variable valve timing system according to claim 1, wherein
the target phase restriction unit restricts the target
opening/closing timing before the command to stop the engine is
issued while the engine is operating.
12. A method for controlling a variable valve timing system that
changes opening/closing timing of at least one of an intake valve
and an exhaust valve provided in an engine, and that includes a
changing mechanism that changes the opening/closing timing by
changing a rotational phase difference between a camshaft, which
drives the valve of which the opening/closing timing is changed,
and a crankshaft by an amount of change corresponding to an
operation amount of an actuator, when the engine is operating,
wherein the changing mechanism sets a ratio of the amount of change
in the opening/closing timing with respect to the operation amount
of the actuator to a lower value when the opening/closing timing is
within a first phase region than when the opening/closing timing is
within a second phase region, comprising: setting target
opening/closing timing of at least one of the intake valve and the
exhaust valve based on an operating state of the engine; setting
the operation amount of the actuator based on a result of
comparison between the target opening/closing timing and the actual
opening/closing timing; and restricting the target opening/closing
timing used when the engine is operating such that the
opening/closing timing is brought into the first phase region by
the time the engine is stopped, by the operation of the actuator
after a command to stop the engine is issued.
13. The method according to claim 12, further comprising:
restricting the target opening/closing timing to the first phase
region when the engine is being started.
14. The method according to claim 12, further comprising:
restricting the target opening/closing timing to a restriction
range that includes the first phase region and a phase region that
has a phase difference of equal to or smaller than a given amount
with the first phase region, when a vehicle is not running.
15. The method according to claim 14, further comprising: setting
the given amount that defines the restriction range to which the
target opening/closing timing is restricted by the target phase
restriction unit based on a temperature of the engine.
16. The method according to claim 15, wherein the given amount is
set to a relatively small value when the temperature of the engine
is low.
17. The method according to claim 12, wherein the first phase
region includes a most delayed phase and a most advanced-side phase
of the first phase region is more delayed than a predetermined
phase, and the target opening/closing timing is set to the
opening/closing timing at the most delayed phase after the command
to stop the engine is issued.
18. The method according to claim 12, wherein the actuator is
formed of an electric motor, and the operation amount of the
actuator corresponds to a rotational speed of the electric motor
relative to a rotational speed of the camshaft.
19. The method according to claim 12, wherein the operating state
of the engine includes an engine speed and an intake air
amount.
20. The method according to claim 19, wherein the target
opening/closing timing is set based on the engine speed and the
intake air amount when the engine is operating under load
conditions.
21. The method according to claim 19, wherein the target
opening/closing timing is set based on the engine speed when the
engine is operating under no-load conditions.
22. The method according to claim 12, wherein the target
opening/closing timing is restricted before the command to stop the
engine is issued while the engine is operating.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to a variable valve timing
system and a method for controlling the same, and, more
specifically, to a variable valve timing system that includes a
mechanism which changes the ratio of the amount of change in the
opening/closing timing of a valve with respect to the operation
amount of an actuator depending on the phase region in which the
opening/closing timing is present, and a method for controlling the
same.
[0003] 2. Description of the Related Art
[0004] A variable valve timing (VVT) system that changes the phase
(i.e., crank angle), at which an intake valve or an exhaust valve
is opened/closed, based on the engine operating state has been
used. Such variable valve timing system changes the phase of the
intake valve or the exhaust valve by rotating a camshaft, which
opens/closes the intake valve or the exhaust valve, relative to,
for example, a sprocket. The camshaft is rotated hydraulically or
by means of an actuator, for example, an electric motor.
[0005] With a variable valve timing system that hydraulically
drives a camshaft, the variable valve timing control is sometimes
not executed as accurately as it should be, in a cold environment
or at the time of start-up of the engine. Such inconvenience is
caused because the hydraulic pressure used to drive the camshaft is
insufficient or the response of the camshaft to the hydraulic
control is slow in such occasions. To obviate such inconveniences,
a variable valve timing system that drives a camshaft by means of
an electric motor has been suggested, as described in, for example,
Japanese Patent Application Publication No. JP-2005-98142
(JP-A-2005-98142), Japanese Patent Application Publication No.
JP-2005-48707 (JP-A-2005-48707), and Japanese Patent Application
Publication No. 2004-156461 (JP-A-2004-156461).
[0006] JP-A-2005-98142 and JP-A-2005-48707 each describe a variable
valve timing system that changes the rotational phase of a camshaft
relative to a crankshaft, namely, the valve timing in accordance
with the rotational phase difference between a sprocket and a guide
rotating body that is rotated by an electric motor. JP-A-2005-98142
describes a mechanism that changes the ratio of the amount of
change in the rotational phase of a camshaft relative to a
crankshaft (valve timing), with respect to the amount of change in
the rotational phase of a guide rotating body relative to a
sprocket depending on the phase region in which the phase of the
valve timing is present. As shown in FIG. 16 in JP-A-2005-98142,
the above-described change-amount ratio is relatively low in the
phase region in which the valve timing is delayed, while the
above-described change-amount ratio is relatively high in the phase
region in which the valve timing is advanced.
[0007] With the configuration described in each of JP-A-2005-98142
and JP-A-2005-48707, the valve timing is changed by reducing the
relative rotational speed between the output shaft of the electric
motor that rotates the guide rotating body and the sprocket at the
speed reduction ratio corresponding to the above-described
change-amount ratio. Namely, with the configuration described in
JP-A-2005-98142, the speed reduction ratio is variably set based on
the phase region in which the phase of the valve timing is
present.
[0008] Accordingly, in the phase region in which the speed
reduction ratio is low, that is, the phase region in which the
amount of change in the valve timing with respect to the relative
rotational speed between the output shaft of the electric motor and
the sprocket is large, the valve timing may be undesirably changed
due to the rotation of the output shaft of the electric motor,
which is caused by a reaction force applied to the camshaft, when
the engine is stopped.
SUMMARY OF THE INVENTION
[0009] The invention provides a variable valve timing system that
prevents occurrence of an undesirable change in the valve timing
when an engine is being stopped, and a method for controlling the
same.
[0010] A first aspect of the invention relates to a variable valve
timing system that changes the opening/closing timing of at least
one of an intake valve and an exhaust valve provided in an engine,
and that includes a changing mechanism, a target phase setting
unit, a phase control unit, and a target phase restriction unit.
The changing mechanism changes the opening/closing timing by
changing the rotational phase difference between a camshaft, which
drives the valve of which the opening/closing timing is changed,
and a crankshaft by an amount of change corresponding to the
operation amount of an actuator, when the engine is operating. The
changing mechanism sets the ratio of the amount of change in the
opening/closing timing with respect to the operation amount of the
actuator to a lower value when the opening/closing timing is within
the first phase region than when the opening/closing timing is
within the second phase region. The target phase setting unit sets
the target opening/closing timing of at least one of the intake
valve and the exhaust valve based on the operating state of the
engine. The phase control unit sets the operation amount of the
actuator based on the result of comparison between the target
opening/closing timing and the actual opening/closing timing. The
target phase restriction unit restricts the target opening/closing
timing used when the engine is operating such that the
opening/closing timing is brought into the first phase region by
the time the engine is stopped, by the operation of the actuator
after a command to stop the engine is issued.
[0011] With the variable valve timing system according to the first
aspect of the invention, the target phase of the opening/closing
timing (hereinafter, sometimes referred to as the "valve timing")
of the valve during the operation of the engine is restricted.
Thus, the valve timing is brought into the first phase region, in
which the ratio of the amount of change in the phase with respect
to the operation amount of the actuator is low (namely, the speed
reduction ratio is high), by the operation of the actuator from
when the command to stop the engine is issued until when the engine
is stopped. As a result, it is possible to prevent occurrence of an
undesirable change in the valve timing when the engine is being
stopped.
[0012] In the first aspect of the invention, the target phase
restriction unit may restrict the target opening/closing timing to
the first phase region when the engine is being started.
[0013] Thus, even when a command to stop the engine is issued in
response to the operation to turn off an ignition switch performed
by the driver while the engine is being started, the valve timing
is maintained within the first phase region. As a result, it is
possible to prevent occurrence of an undesirable change in the
valve timing.
[0014] In the first aspect of the invention, the target phase
restriction unit may restrict the target opening/closing timing to
a restriction range that includes the first phase region and a
phase region that has a phase difference of equal to or smaller
than a given amount with the first phase region, when a vehicle is
not running.
[0015] Thus, when the vehicle is not running, namely, when there is
a high possibility that an engine stop command is issued in
response to the operation performed by the driver to turn off the
ignition switch or an engine stop command is automatically issued
in a vehicle in which the engine intermittent operation is
performed such as a hybrid vehicle, the valve timing is prevented
from being apart from the first phase region by a large amount.
Accordingly, when an engine stop command is issued while the
vehicle is not running, the valve timing is reliably brought into
the first phase region by the time the engine is stopped. As a
result, it is possible to prevent occurrence of an undesirable
change in the valve timing when the engine is being stopped.
[0016] In the first aspect of the invention, the variable valve
timing system may further include a variable restriction range
setting unit. The variable restriction range setting unit sets the
given amount that defines the restriction range, to which the
target opening/closing timing is restricted by the target phase
restriction unit, based on a temperature of the engine. The
variable restriction range setting unit may set the given amount to
a relatively small value when the temperature of the engine is
low.
[0017] Thus, even when the engine temperature is low, that is, when
it is difficult to achieve the required operation amount of the
actuator and the required rate of change in the valve timing due to
an increase in the viscosity of the lubricating oil, the valve
timing is restricted to the restriction range that includes the
first phase region. As a result, even when the temperature of the
engine is low, it is possible to prevent occurrence of an
undesirable change in the valve timing when the engine is being
stopped.
[0018] In the first aspect of the invention, the first phase region
may include the most delayed phase and the most advanced-side phase
of the first phase region may be more delayed than a predetermined
phase, and the target phase setting unit may set the target
opening/closing timing to the opening/closing timing at the most
delayed phase after the command to stop the engine is issued.
[0019] Thus, even when the start-time pressure reduction control is
executed to suppress vibration of the engine by reducing a torque
produced by the initial expansion of the air-fuel mixture that
takes place in the engine while the engine is being started, it is
possible to prevent occurrence of an undesirable change in the
valve timing when the engine is being stopped.
[0020] In the first aspect of the invention, the actuator may be
formed of an electric motor, and the operation amount of the
actuator may correspond to the rotational speed of the electric
motor relative to the rotational speed of the camshaft.
[0021] Thus, when the actuator is formed of the electric motor and
the operation amount of the actuator corresponds to the rotational
speed of the electric motor relative to the rotational speed of the
camshaft, it is possible to prevent occurrence of an undesirable
change in the valve timing when the engine is being stopped.
[0022] A second aspect of the invention relates to a method for
controlling a variable valve timing system that changes the
opening/closing timing of at least one of an intake valve and an
exhaust valve provided in an engine, and that includes a changing
mechanism that changes the opening/closing timing by changing the
rotational phase difference between a camshaft, which drives the
valve of which the opening/closing timing is changed, and a
crankshaft by an amount of change corresponding to the operation
amount of an actuator, when the engine is operating. The changing
mechanism sets the ratio of the amount of change in the
opening/closing timing with respect to the operation amount of the
actuator to a lower value when the opening/closing timing is within
the first phase region than when the opening/closing timing is
within the second phase region. According to the method, the target
opening/closing timing of at least one of the intake valve and the
exhaust valve is set based on the operating state of the engine,
and the operation amount of the actuator is set based on the result
of comparison between the target opening/closing timing and the
actual opening/closing timing. The target opening/closing timing
used when the engine is, operating is restricted such that the
opening/closing timing is brought into the first phase region by
the time the engine is stopped, by the operation of the actuator
after a command to stop the engine is issued.
[0023] With the variable valve timing system and the method for
controlling the same according to the aspects of the invention
described above, it is possible to prevent occurrence of an
undesirable change in the valve timing when the engine is being
stopped
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The foregoing and further objects, features and advantages
of the invention will become apparent from the following
description of an example embodiment with reference to the
accompanying drawings, wherein the same or corresponding portions
will be denoted by the same reference numerals and wherein:
[0025] FIG. 1 is a view schematically showing the structure of a
vehicle engine provided with a variable valve timing system
according to an embodiment of the invention;
[0026] FIG. 2 is a graph showing the map that defines the phase of
an intake camshaft;
[0027] FIG. 3 is a cross-sectional view showing an intake VVT
mechanism;
[0028] FIG. 4 is a cross-sectional view taken along the line IV-IV
in FIG. 3;
[0029] FIG. 5 is a first cross-sectional view taken along the line
V-V in FIG. 3;
[0030] FIG. 6 is a second cross-sectional view taken along the line
V-V in FIG. 3;
[0031] FIG. 7 is a cross-sectional view taken along the line
VII-VII in FIG. 3;
[0032] FIG. 8 is a cross-sectional view taken along the line in
FIG. 3;
[0033] FIG. 9 is a graph showing the speed reduction ratio that the
elements of the intake VVT mechanism realize in cooperation;
[0034] FIG. 10 is a graph showing the relationship between the
phase of a guide plate relative to a sprocket and the phase of the
intake camshaft;
[0035] FIG. 11 is a schematic block diagram illustrating the
configuration of the control over the phase of an intake valve,
executed by the variable valve timing system according to the
embodiment of the invention;
[0036] FIG. 12 is a block diagram illustrating the control over the
rotational speed of an electric motor that serves as an actuator of
the variable valve timing system according to the embodiment of the
invention;
[0037] FIG. 13 is a graph illustrating the control over the
rotational speed of the electric motor;
[0038] FIG. 14 is a graph illustrating the control over the phase
of the intake valve, which is executed when the engine is
started;
[0039] FIG. 15 is a first flowchart illustrating the operation of a
target phase restriction unit and a restriction range setting unit
shown in FIG. 12;
[0040] FIG. 16 is a second flowchart illustrating the operation of
the target phase restriction unit and a restriction range setting
unit;
[0041] FIG. 17 is a graph illustrating the manner in which the
target phase value is restricted by the target phase restriction
unit and the restriction range setting unit; and
[0042] FIG. 18 is a graph illustrating the manner in which the
restriction range of the target phase value is variably set by the
restriction range setting unit.
DETAILED DESCRIPTION OF THE EMBODIMENT
[0043] Hereafter, an embodiment of the invention will be described
with reference to the accompanying drawings. In the following
description, the same or corresponding elements will be denoted by
the same reference numerals. The names and functions of the
elements having the same reference numerals are also the same.
Accordingly, the descriptions concerning the elements having the
same reference numerals will be provided only once below.
[0044] First, a vehicle engine provided with a variable valve
timing system according to the embodiment of the invention will be
described with reference to FIG. 1.
[0045] An engine 1000 is an eight-cylinder V-type engine including
a first bank 1010 and a second bank 1012 each of which has four
cylinders therein. Note that, the variable valve timing system
according to the embodiment of the invention may be applied to any
types of engines. Namely, the variable valve timing system may be
applied to engines other than an eight-cylinder V-type engine.
[0046] Air that has passed through an air cleaner 1020 is supplied
to the engine 1000. A throttle valve 1030 adjusts the amount of air
supplied to the engine 1000. The throttle valve 1030 is an
electronically-controlled throttle valve that is driven by a
motor.
[0047] The air is introduced into a cylinder 1040 through an intake
passage 1032. The air is then mixed with fuel in a combustion
chamber formed within the cylinder 1040. The fuel is injected from
an injector 1050 directly into the cylinder 1040. Namely, the
injection hole of the injector 1050 is positioned within the
cylinder 1040.
[0048] The fuel is injected into the cylinder 1040 in the intake
stroke. The time at which the fuel is injected need not be in the
intake stroke. The description concerning the embodiment of the
invention will be provided on the assumption that the engine 1000
is a direct-injection engine where the injection hole of the
injector 1050 is positioned within the cylinder 1040. In addition
to the injector 1050 for direct-injection, an injector for
port-injection may be provided. Alternatively, only an injector for
port-injection may be provided.
[0049] The air-fuel mixture in the cylinder 1040 is ignited by a
spark plug 1060, and then burned. The burned air-fuel mixture,
namely, the exhaust gas is purified by a three-way catalyst 1070,
and then discharged to the outside of the vehicle. A piston 1080 is
pushed down due to combustion of the air-fuel mixture, whereby a
crankshaft 1090 is rotated.
[0050] An intake valve 1100 and an exhaust valve 1110 are provided
on the top of the cylinder 1040. The intake valve 1100 is driven by
an intake camshaft 1120, and the exhaust valve 1110 is driven by an
exhaust camshaft 1130. The intake camshaft 1120 and the exhaust
camshaft 1130 are connected to each other by, for example, a chain
or a gear, and rotate at the same number of revolutions (at
one-half the number of revolutions of the crankshaft 1090). Because
the number of revolutions (typically, the number of revolutions per
minute (rpm)) of a rotating body, for example, a shaft is usually
referred to as the rotational speed, the term "rotational speed"
will be used in the following description.
[0051] The phase (opening/closing timing) of the intake valve 1100
is controlled by an intake VVT mechanism 2000 which is fitted to
the intake camshaft 1120. The phase (opening/closing timing) of the
exhaust valve 1110 is controlled by an exhaust VVT mechanism 3000
which is fitted to the exhaust camshaft 1130.
[0052] In the embodiment of the invention, the intake camshaft 1120
and the exhaust camshaft 1130 are rotated by the VVT mechanisms
2000 and 3000, respectively, whereby the phase of the intake valve
1100 and the phase of the exhaust valve 1110 are controlled.
However, the method for controlling the phase is not limited to
this.
[0053] The intake VVT mechanism 2000 is operated by an electric
motor 2060 (shown in FIG. 3). The electric motor 2060 is controlled
by an electronic control unit (ECU) 4000. The magnitude of electric
current passing through the electric motor 2060 is detected by an
ammeter (not shown) and the voltage applied to the electric motor
2060 is detected by a voltmeter (not shown), and a signal
indicating the magnitude of electric current and a signal
indicating the voltage are transmitted to the ECU 4000.
[0054] The exhaust VVT mechanism 3000 is hydraulically operated.
Note that, the intake VVT mechanism 2000 may be hydraulically
operated. Note that, the exhaust VVT mechanism 3000 may be operated
by means of an electric motor.
[0055] The ECU 4000 receives signals indicating the rotational
speed and the crank angle of the crankshaft 1090, from a crank
angle sensor 5000. The ECU 4000 also receives a signal indicating
the phase of the intake camshaft 1120 and a signal indicating the
phase of the exhaust camshaft 1130 (the positions of these
camshafts in the rotational direction), from a camshaft position
sensor 5010.
[0056] In addition, the ECU 4000 receives a signal indicating the
temperature of a coolant for the engine 1000 (the coolant
temperature) from a coolant temperature sensor 5020, and a signal,
indicating the amount of air supplied to the engine 1000, from an
airflow meter 5030.
[0057] The ECU 4000 controls the throttle valve opening amount, the
ignition timing, the fuel injection timing, the fuel injection
amount, the phase of the intake valve 1100, the phase of the
exhaust valve 1110, etc. based on the signals received from the
above-mentioned sensors and the maps and programs stored in memory
(not shown) so that the engine 1000 is brought into the desired
operating state.
[0058] According to the embodiment of the invention, the ECU 4000
sets the target phase of the intake valve 1100, which corresponds
to the current engine operating state, based on the map that uses
parameters indicating the engine operating state, typically, the
map that uses the engine speed NE and the intake air amount KL as
parameters. Generally, multiple maps, used to set the phase of the
intake valve 1100 at multiple coolant temperatures, are stored in
the memory.
[0059] Hereafter, the intake VVT mechanism 2000 will be described
in more detail. Note that, the exhaust VVT mechanism 3000 may have
the same structure as the intake VVT mechanism 2000 described
below. Alternatively, each of the intake VVT mechanism 2000 and the
exhaust VVT mechanism 3000 may have the same structure as the
intake VVT mechanism 2000 described below.
[0060] As shown in FIG. 3, the intake VVT mechanism 2000 includes a
sprocket 2010, a cam plate 2020, link mechanisms 2030, a guide
plate 2040, a speed reducer 2050, and the electric motor 2060.
[0061] The sprocket 2010 is connected to the crankshaft 1090 via,
for example, a chain. The rotational speed of the sprocket 2010 is
one-half the rotational speed of the crankshaft 1090, as in the
case of the intake camshaft 1120 and the exhaust camshaft 1130. The
intake camshaft 1120 is provided such that the intake camshaft 1120
is coaxial with the sprocket 2010 and rotates relative to the
sprocket 2010.
[0062] The cam plate 2020 is connected to the intake camshaft 1120
with a first pin 2070. In the sprocket 2010, the cam plate 2020
rotates together with the intake camshaft 1120. The cam plate 2020
and the intake camshaft 1120 may be formed integrally with each
other.
[0063] Each link mechanism 2030 is formed of a first arm 2031 and a
second arm 2032. As shown in FIG. 4, that is, a cross-sectional
view taken along the line IV-IV in FIG. 3, paired first arms 2031
are arranged in the sprocket 2010 so as to be symmetric with
respect to the axis of the intake camshaft 1120. Each first arm
2031 is connected to the sprocket 2010 so as to pivot about a
second pin 2072.
[0064] As shown in FIG. 5, that is, a cross-sectional view taken
along the line V-V in FIG. 3, and FIG. 6 that shows the state
achieved by advancing the phase of the intake valve 1100 from the
state shown in FIG. 5, the first arms 2031 and the cam plate 2020
are connected to each other by the second arms 2032.
[0065] Each second arm 2032 is supported so as to pivot about a
third pin 2074, with respect to the first arm 2031. Each second arm
2032 is supported so as to pivot about a fourth pin 2076, with
respect to the cam plate 2020.
[0066] The intake camshaft 1120 is rotated relative to the sprocket
2010 by the pair of link mechanisms 2030, whereby the phase of the
intake valve 100 is changed. Accordingly, even if one of the link
mechanisms 2030 breaks and snaps, the phase of the intake valve
1100 is changed by the other link mechanism 2030.
[0067] As shown in FIG. 3, a control pin 2034 is fitted on one face
of each link mechanism 2030 (more specifically, the second arm
2032), the face being proximal to the guide plate 2040. The control
pin 2034 is arranged coaxially with the third pin 2074. Each
control pin 2034 slides within a guide groove 2042 formed in the
guide plate 2040.
[0068] Each control pin 2034 moves in the radial direction while
sliding within the guide groove 2042 formed in the guide plate
2040. The movement of each control pin 2034 in the radial direction
rotates the intake camshaft 1120 relative to the sprocket 2010.
[0069] As shown in FIG. 7, that is, a cross-sectional view taken
along the line VII-VII in FIG. 3, the guide groove 2042 is formed
in a spiral fashion such that the control pin 2034 moves in the
radial direction in accordance with the rotation of the guide plate
2040. However, the shape of the guide groove 2042 is not limited to
this.
[0070] As the distance between the control pin 2034 and the axis of
the guide plate 2040 increases in the radial direction, the phase
of the intake valve 1100 is more delayed. Namely, the amount of
change in the phase corresponds to the amount by which each link
mechanism 2030 is operated in accordance with the movement of the
control pin 2034 in the radial direction. Note that, as the
distance between the control pin 2034 and the axis of the guide
plate 2040 increases in the radial direction, the phase of the
intake valve 1100 may be more advanced.
[0071] As shown in FIG. 7, when the control pin 2034 reaches the
end of the guide groove 2042, the operation of the link mechanism
2030 is restricted. Accordingly, the phase at which the control pin
2034 reaches the end of the guide groove 2042 is the most advanced
phase or the most delayed phase of the intake valve 1100.
[0072] As shown in FIG. 3, multiple recesses 2044 are formed in one
face of the guide plate 2040, the face being proximal to the speed
reducer 2050. The recesses 2044 are used to connect the guide plate
2040 and the speed reducer 2050 to each other.
[0073] The speed reducer 2050 is formed of an externally-toothed
gear 2052 and an internally-toothed gear 2054. The
externally-toothed gear 2052 is fixed to the sprocket 2010 so as to
rotate together with the sprocket 2010.
[0074] Multiple projections 2056, which are fitted in the recesses
2044 of the guide plate 2040, are formed on the internally-toothed
gear 2054. The internally-toothed gear 2054 is supported so as to
be rotatable about an eccentric axis 2066 of a coupling 2062 of
which the axis deviates from an axis 2064 of the output shaft of
the electric motor 2060.
[0075] FIG. 8 shows a cross-sectional view taken along the line in
FIG. 3. The internally-toothed gear 2054 is arranged such that part
of the multiple teeth thereof mesh with the externally-toothed gear
2052. When the rotational speed of the output shaft of the electric
motor 2060 is equal to the rotational speed of the sprocket 2010,
the coupling 2062 and the internally-toothed gear 2054 rotate at
the same rotational speed as the externally-toothed gear 2052 (the
sprocket 2010). In this case, the guide plate 2040 rotates at the
same rotational speed as the sprocket 2010, and the phase of the
intake valve 1100 is maintained.
[0076] When the coupling 2062 is rotated about the axis 2064
relative to the externally-toothed gear 2052 by the electric motor
2060, the entirety of the internally-toothed gear 2054 turns around
the axis 2064, and, at the same time, the internally-toothed gear
2054 rotates about the eccentric axis 2066. The rotational movement
of the internally-toothed gear 2054 causes the guide plate 2040 to
rotate relative to the sprocket 2010, whereby the phase of the
intake valve 1100 is changed.
[0077] As can be seen from the structure described above, it is
difficult to change the phase of the intake valve 1100 by solely
rotating the internally-toothed gear 2054 using the electric motor
2060 when the engine 1000 is stopped, namely, when the rotation of
the sprocket 2010 is stopped. That is, it is difficult for the
intake VVT mechanism 2000 to change the valve timing after the
engine 1000 is stopped.
[0078] The phase of the intake valve 1100 is changed by reducing
the relative rotational speed (the operation amount of the electric
motor 2060) between the output shaft of the electric motor 2060 and
the sprocket 2010 using the speed reducer 2050, the guide plate
2040 and the link mechanisms 2030. Alternatively, the phase of the
intake valve 1100 may be changed by increasing the relative
rotational speed between the output shaft of the electric motor
2060 and the sprocket 2010. The output shaft of the electric motor
2060 is provided with a motor rotational angle sensor 5050 that
outputs a signal indicating the rotational angle (the position of
the output shaft in its rotational direction) of the output shaft.
Generally, the motor rotational angle sensor 5050 produces a pulse
signal each time the output shaft of the electric motor 2060 is
rotated by a predetermined angle. The rotational speed of the
output shaft of the electric motor 2060 (hereinafter, simply
referred to as the "rotational speed of the electric motor 2060"
where appropriate) is detected based on the signal output from the
motor rotational angle sensor 5050.
[0079] As shown in FIG. 9, the speed reduction ratio R (.theta.)
that the elements of the intake VVT mechanism 2000 realize in
cooperation, namely, the ratio of the relative rotational speed
between the output shaft of the electric motor 2060 and the
sprocket 2010 to the amount of change in the phase of the intake
valve 1100 may take a value corresponding to the phase of the
intake valve 1100. According to the embodiment of the invention, as
the speed reduction ratio increases, the amount of change in the
phase with respect to the relative rotational speed between the
output shaft of the electric motor 2060 and the sprocket 2010
decreases.
[0080] When the phase of the intake valve 1100 is within a phase
region 2500 that extends from the most delayed phase to CA1, the
speed reduction ratio that the elements of the intake VVT mechanism
2000 realize in cooperation is R1. When the phase of the intake
valve 1100 is within a phase region 2520 that extends from CA2 (CA2
is the phase more advanced than CA1) to the most advanced phase,
the speed reduction ratio that the elements of the intake VVT
mechanism 2000 realize in cooperation is R2 (R1>R2).
[0081] When the phase of the intake valve 1100 is within a phase
region 2510 that extends from CA1 to CA2, the speed reduction ratio
that the elements of the intake VVT mechanism 2000 realize in
cooperation changes at a predetermined rate
((R2-R1)/(CA2-CA1)).
[0082] The effects of the thus configured intake VVT mechanism 2000
of the variable valve timing system according to the embodiment of
the invention will be described below.
[0083] When the phase of the intake valve 1100 (the intake camshaft
1120) is advanced, the electric motor 2060 is operated to rotate
the guide plate 2040 relative to the sprocket 2010. As a result,
the phase of the intake valve 1100 is advanced, as shown in FIG.
10.
[0084] When the phase of the intake valve 1100 is within the phase
region 2500 that extends from the most delayed phase to CA1, the
relative rotational speed between the output shaft of the electric
motor 2060 and the sprocket 2010 is reduced at the speed reduction
ratio R1. As a result, the phase of the intake valve 1100 is
advanced.
[0085] When the phase of the intake valve 1100 is within the phase
region 2520 that extends from CA2 to the most advanced phase, the
relative rotational speed between the output shaft of the electric
motor 2060 and the sprocket 2010 is reduced at the speed reduction
ratio R2. As a result, the phase of the intake valve 1100 is
advanced.
[0086] When the phase of the intake valve 1100 is delayed, the
output shaft of the electric motor 2060 is rotated relative to the
sprocket 2010 in the direction opposite to the direction in which
the phase of the intake valve 1100 is advanced. When the phase is
delayed, the relative rotational speed between the output shaft of
the electric motor 2060 and the sprocket 2010 is reduced in the
manner similar to that when the phase is advanced. When the phase
of the intake valve 1100 is within the phase region 2500 that
extends from the most delayed phase to CA1, the relative rotational
speed between the output shaft of the electric motor 2060 and the
sprocket 2010 is reduced at the speed reduction ratio R1. As a
result, the phase is delayed. When the phase of the intake valve
1100 is within the phase region 2520 that extends from CA2 to the
most advanced phase, the relative rotational speed between the
output shaft of the electric motor 2060 and the sprocket 2010 is
reduced at the speed reduction ratio R2. As a result, the phase is
delayed.
[0087] Accordingly, as long as the direction of the relative
rotation between the output shaft of the electric motor 2060 and
the sprocket 2010 remains unchanged, the phase of the intake valve
1100 may be advanced or delayed in both the phase region 2500 that
extends from the most delayed phase to CA1 and the phase region
2520 that extends from the CA2 to the most advanced phase. In this
case, in the phase region 2520 that extends from CA2 to the most
advanced phase, the phase is advanced or delayed by an amount
larger than that in the phase region 2500 that extends from the
most delayed phase to CA1. Accordingly, the phase region 2520 is
broader in the phase change width than the phase region 2500.
[0088] In the phase region 2500 that extends from the most delayed
phase to CA1, the speed reduction ratio is high. Accordingly, a
high torque is required to rotate the output shaft of the electric
motor 2060 using the torque applied to the intake camshaft 1120 in
accordance with the operation of the engine 1000. Therefore, even
when the electric motor 2060 does not produce a torque, for
example, even when the electric motor 2060 is not operating, the
rotation of the output shaft of the electric motor 2060, which is
caused by the torque applied to the intake camshaft 1120, is
restricted. This restricts occurrence of an undesirable phase
change, that is, the deviation of the actual phase from the phase
used in the control.
[0089] Preferably, the relationship between the direction in which
the electric motor 2060 rotates relative to the sprocket 2010 and
the advance/delay of the phase is set such that the phase of the
intake valve 1100 is delayed when the output shaft of the electric
motor 2060 is lower in rotational speed than the sprocket 2010.
Thus, when the electric motor 2060 that serves as the actuator
becomes inoperative while the engine is operating, the phase of the
intake valve 1100 is gradually delayed, and finally agrees with the
most delayed phase. Namely, even if the intake valve phase control
becomes inexecutable, the phase of the intake valve 1100 is brought
into a state in which combustion stably takes place in the engine
1000.
[0090] When the phase of the intake valve 1100 is within the phase
region 2510 that extends from CA1 to CA2, the relative rotational
speed between the output shaft of the electric motor 2060 and the
sprocket 2010 is reduced at the speed reduction ratio that changes
at a predetermined rate. As a result, the phase of the intake valve
1100 is advanced or delayed.
[0091] When the phase of the intake valve 1100 is shifted from the
phase region 2500 to the phase region 2520, or from the phase
region 2520 to the phase region 2500, the amount of change in the
phase with respect to the relative rotational speed between the
output shaft of the electric motor 2060 and the sprocket 2010 is
gradually increased or reduced. Accordingly, an abrupt stepwise
change in the amount of change in the phase is restricted to
restrict an abrupt change in the phase. As a result, the phase of
the intake valve 1100 is controlled more appropriately.
[0092] The speed reduction ratio R(.theta.) in FIG. 9 corresponds
to the reciprocal of the ratio of the amount of change in the phase
of the intake valve 1100 with respect to the operation amount of
the electric motor 2060 (the relative rotational speed between the
output shaft of the electric motor 2060 and the sprocket 2010).
Namely, the phase region 2500 in which the speed reduction ratio is
high may be regarded as a "first phase region" according to the
invention, and the other phase regions 2510 and 2520 may be
collectively regarded as a "second phase region" according to the
invention.
[0093] With the intake VVT mechanism 2000 of the variable valve
timing system according to the embodiment of the invention, when
the phase of the intake valve 1100 is within the phase region 2500
that extends from the most delayed phase to CA1, the speed
reduction ratio that the elements of the intake VVT mechanism 2000
realize in cooperation is R1. When the phase of the intake valve
1100 is within the phase region 2520 that extends from CA2 to the
most advanced phase, the speed reduction ratio that the elements of
the intake VVT mechanism 2000 realize in cooperation is R2 that is
lower than R1. Accordingly, as long as the direction in which the
output shaft of the electric motor 2060 remains unchanged, the
phase of the intake valve 1100 may be advanced or delayed in both
the phase region 2500 that extends from the most delayed phase to
CA1 and the phase region 2520 that extends from the CA2 to the most
advanced phase. In this case, in the phase region 2520 that extends
from CA2 to the most advanced phase, the phase is advanced or
delayed by an amount larger than that in the phase region 2500 that
extends from the most delayed phase to CA1. Accordingly, the phase
region 2520 is broader in the phase change width than the phase
region 2500. In the phase region 2500 that extends from the most
delayed phase to CA1, the speed reduction ratio is high.
Accordingly, rotation of the output shaft of the electric motor
2060, which is caused by a torque applied to the intake camshaft
1120 in accordance with the operation of the engine, is restricted.
This restricts the deviation of the actual phase from the phase
used in the control. As a result, it is possible to change the
phase in a broader range, and to control the phase more
accurately.
[0094] Next, the configuration of the control over the phase of the
intake valve 1100 (hereinafter, simply referred to as the "intake
valve phase" where appropriate) will be described in detail.
[0095] As shown in FIG. 11, the engine 1000 is configured such that
the power is transferred from the crank shaft 1090 to the intake
camshaft 1120 and the exhaust camshaft 1130 via the sprocket 2010
and a sprocket 2012, respectively, by a timing chain 1200 (or a
timing belt), as previously described with reference to FIG. 1. The
camshaft position sensor 5010 that outputs a cam angle signal Piv
each time the intake camshaft 1120 rotates by a predetermined cam
angle is fitted on the outer periphery of the intake camshaft 1120.
The crank angle sensor 5000 that outputs a crank angle signal Pca
each time the crankshaft 1090 rotates by a predetermined crank
angle is fitted on the outer periphery of the crankshaft 1090. The
motor rotational angle sensor 5050 that outputs a motor rotational
angle signal Pmt each time the electric motor 2060 rotates by a
predetermined rotational angle is fitted to a rotor (not shown) of
the electric motor 2060. These cam angle signal Ply, crank angle
signal Pca and motor rotational angle signal Pmt are transmitted to
the ECU 4000.
[0096] The ECU 4000 controls the operation of the engine 1000 based
on the signals output from the sensors that detect the operating
state of the engine 1000 and the operation conditions (the pedal
operations performed by the driver, the current vehicle speed,
etc.) such that the engine 1000 produces a required output power.
As part of the engine control, the ECU 4000 sets the target phase
of the intake valve 1100 and the target phase of the exhaust valve
1110 based on the map shown in FIG. 2. In addition, the ECU 4000
prepares the rotational speed command value Nmref for the electric
motor 2060 that serves as the actuator for the intake VVT mechanism
2000. If the electric motor 2060 rotates at the rotational speed
command value Nmref, the phase of the intake valve 1100 matches the
target phase.
[0097] The rotational speed command value Nmref is set based on the
relative rotational speed between the output shaft of the electric
motor 2060 and the sprocket 2010 (the intake camshaft 1120), which
corresponds to the operation amount of the actuator, as described
in detail below. An electric-motor EDU (Electronic Drive Unit) 4100
controls the rotational speed of the electric motor 2060 based on
the rotational speed command value Nmref indicated by a signal from
the ECU 4000.
[0098] When the engine 1000 is going to stop, more specifically,
after a command to stop the engine 1000 is issued, the target value
of the phase (target phase) of the intake valve 1100 (hereinafter,
referred to as the "intake valve phase" where appropriate) is set
to the stop-time phase that is suitable for start-up of the engine
in order to facilitate the subsequent engine starting. Namely, if
it is determined that the intake valve phase differs from the
stop-time phase (i.e., if the stop-time phase has not been
achieved) when a command to stop the engine 1000 is issued, the
variable valve timing system needs to change the intake valve
phase.
[0099] FIG. 12 is a block diagram illustrating the control over the
rotational speed of an electric motor 2060 that serves as the
actuator of the intake VVT mechanism 2000 according to the
embodiment of the invention.
[0100] As shown in FIG. 12, a target phase setting unit 4010 sets
the target phase value IVref for the intake valve 1100, which is
the target of the variable valve timing control, based on the
parameters indicating the engine operating state, with reference to
an on-load operation map 4012 that is used during the load
operation, and a no-load operation map 4014 that is used during the
no-load operation. Each of the on-load operation map 4012 and the
no-load operation map 4014 is prepared for each of multiple engine
temperatures (more specifically, coolant temperatures). For
example, with reference to the on-load operation map 4012, the
target phase value IVref is set based on the engine speed and the
intake air amount, as shown in FIG. 2. With reference to the
no-load operation map 4014, the target phase value IVref is set
based on the engine speed.
[0101] A target phase restriction unit 4020 restricts the target
phase value IVref in the predetermined engine operating state
(typically, in the operating state in which an engine stop command
may be issued, for example, when the engine is being started or
when the vehicle is not running), such that the intake valve phase
is reliably brought into the phase region 2500, in which the speed
reduction is high, by the time the engine is stopped. As described
below in detail, the target phase restriction unit 4020 restricts
the target phase value IVref to a restriction range. When the
target phase value IVref is within the restriction range, the
intake valve phase is reliably returned to the phase region 2500 by
the operation of the electric motor 2060 during the period from
when an engine stop command is issued until when the engine is
stopped. A restriction range setting unit 4030 variably sets the
restriction range used by the target phase restriction unit 4020
based on the coolant temperature that indicates the engine
temperature.
[0102] As described above, the target phase value IVref of the
intake valve 1100 is basically set by the target phase setting unit
4010 based on the engine operating state. In addition, in the
operating state in which an engine stop command may be issued, the
target phase value IVref is restricted by the target phase
restriction unit 4020 and the restriction range setting unit
4030.
[0103] An actuator operation amount setting unit 6000 prepares the
rotational speed command value Nmref for the electric motor 2060
based on the deviation of the current actual phase IV(.theta.) of
the intake valve 1100 (hereinafter, referred to as the "actual
intake valve phase IV(.theta.)" where appropriate) from the target
phase value IVref. The rotational speed command value Nmref is set
such that the actuator operation amount at which the actual intake
valve phase IV(.theta.) matches the target phase value IVref is
achieved.
[0104] The actuator operation amount setting unit 6000 includes a
valve phase detection unit 6010; a camshaft phase change amount
calculation unit 6020; a relative rotational speed setting unit
6030; a camshaft rotational speed detection unit 6040; and a
rotational speed command value preparation unit 6050. The function
of the actuator operation amount setting unit 6000 is exhibited by
executing the control routines stored in advance in the ECU 4000 in
predetermined control cycles.
[0105] The valve phase detection unit 6010 calculates the actual
intake valve phase IV(.theta.) based on the crank angle signal Pca
from the crank angle sensor 5000, the cam angle signal Ply from the
camshaft position sensor 5010, and the motor rotational angle
signal Pmt from the rotational angle sensor 5050 for the electric
motor 2060.
[0106] The camshaft phase change amount calculation unit 6020
includes a calculation unit 6022 and a required phase change amount
calculation unit 6025. The calculation unit 6022 calculates the
deviation .DELTA.IV(.theta.) (.DELTA.IV(.theta.)=IV(.theta.)-IVref)
of the intake valve phase IV(.theta.) from the target phase value
IVref. The required phase change amount calculation unit 6025
calculates the amount .DELTA..theta. by which the phase of the
intake camshaft 1120 is required to change in the current control
cycle based on the deviation .DELTA.IV(.theta.) calculated by the
calculation unit 6022.
[0107] For example, the maximum value .DELTA..theta.max of the
phase change amount AG in a single control cycle is set in advance.
The required phase change amount calculation unit 6025 sets the
phase change amount .DELTA..theta., which corresponds to the
deviation .DELTA.IV(.theta.) and which is equal to or smaller than
the maximum value .DELTA..theta.max. The maximum value
.DELTA..theta.max may be a fixed value. Alternatively, the maximum
value .DELTA..theta.max may be variably set by the required phase
change amount calculation unit 6025 based on the operating state of
the engine 1000 (the engine speed, the intake air amount, etc.) and
the degree of the deviation .DELTA.IV(.theta.). The camshaft phase
change amount calculation unit 6020 determines whether the intake
valve phase IV(.theta.) has reached the target phase value IVref.
If it is determined that the intake valve phase N(.theta.) has
reached the target phase value IVref, the camshaft phase change
amount calculation unit 6020 sets the phase change amount
.DELTA..theta. to zero (.DELTA..theta.=0).
[0108] The relative rotational speed setting unit 6030 calculates
the rotational speed .DELTA.Nm of the output shaft of the electric
motor 2060 relative to the rotational speed of the sprocket 2010
(the intake camshaft 1120). The rotational speed .DELTA.Nm needs to
be achieved in order to obtain the required phase change amount
.DELTA..theta. calculated by the required phase change amount
calculation unit 6025. For example, the relative rotational speed
.DELTA.Nm is set to a positive value (.DELTA.Nm>0) when the
phase of the intake valve 1100 is advanced. On the other hand, when
the phase of the intake valve 1100 is delayed, the relative
rotational speed .DELTA.Nm is set to a negative value
(.DELTA.Nm<0). When the current phase of the intake valve 1100
is maintained (.DELTA..theta.=0), the relative rotational speed
.DELTA.Nm is set to a value substantially equal to zero
(.DELTA.Nm=0).
[0109] The relationship between the phase change amount
.DELTA..theta. per unit time .DELTA.T corresponding to one control
cycle and the relative rotational speed .DELTA.Nm is expressed by
Equation 1 shown below. In Equation 1, R(.theta.) is the speed
reduction ratio that changes in accordance with the phase of the
intake valve 1100, as shown in FIG. 9.
.DELTA..theta..varies..DELTA.Nm.times.360.degree..times.(1/R(.theta.)).t-
imes..DELTA.T Equation 1
According to Equation 1, the relative rotational speed setting unit
6030 calculates the rotational speed .DELTA.Nm of the electric
motor 2060 relative to the rotational speed of the sprocket 2010,
the relative rotational speed .DELTA.Nm being required to be
achieved to obtain the required phase change amount .DELTA..theta.
of the camshaft during the control cycle .DELTA.T.
[0110] The camshaft rotational speed detection unit 6040 calculates
the rotational speed of the sprocket 2010, namely, the actual
rotational speed IVN of the intake camshaft 1120 by dividing the
rotational speed of the crankshaft 1090 by two. Alternatively, the
camshaft rotational speed detection unit 6040 may calculate the
actual rotational speed IVN of the intake camshaft 1120 based on
the cam angle signal Piv from the camshaft position sensor 5010.
Generally, the number of cam angle signals output during one
rotation of the intake camshaft 1120 is smaller than the number of
crank angle signals output during one rotation of the crankshaft
1090. Accordingly, the accuracy of detection is enhanced by
detecting the camshaft rotational speed PIN based on the rotational
speed of the crankshaft 1090.
[0111] The rotational speed command value preparation unit 6050
prepares the rotational speed command value Nmref for the electric
motor 2060 by adding the actual rotational speed IVN of the intake
camshaft 1120, which is calculated by the camshaft rotational speed
detection unit 6040, to the relative rotational speed .DELTA.Nm set
by the relative rotational speed setting unit 6030. A signal
indicating the rotational speed command value Nmref prepared by the
rotational speed command value preparation unit 6050 is transmitted
to the electric-motor EDU 4100.
[0112] The electric-motor ECU 4100 is connected to a power supply
4200 via a relay circuit 4250. The on/off state of the relay
circuit 4250 is controlled based on the control signal SRL. The
power supply 4200 is usually formed of a secondary battery that is
electrifiable when the engine is operating.
[0113] The electric-motor EDU 4100 executes the rotational speed
control such that the rotational speed of the electric motor 2060
matches the rotational speed command value Nmref. For example, the
electric-motor EDU 4100 controls the on/off state of a power
semiconductor element (e.g. a transistor) to control the electric
power supplied to the electric motor 2060 (typically, the magnitude
of electric current Imt passing through the electric motor and the
amplitude of the voltage applied to the electric motor) based on
the deviation (Nmref-Nm) of the actual rotational speed Nm of the
electric motor 2060 from the rotational speed command value Nmref.
For example, the duty ratio used in the on/off operation of the
power semiconductor element is controlled.
[0114] The electric-motor EDU 4100 controls the duty ratio DTY that
is adjustment amount used in the rotational speed control according
to Equation 2 indicated below, in order to control the electric
motor 2060 more appropriately.
DTY=DTY(ST)+DTY(FB) Equation 2
[0115] In Equation 2, DTY(FB) is a feedback term based on the
control calculation using the above-described deviation and a
predetermined control gain (typically, common P control or PI
control).
[0116] DTY(ST) in Equation 2 is a preset term that is set based on
the rotational speed command value Nmref for the electric motor
2060 and the set relative rotational speed .DELTA.Nm, as shown in
FIG. 13.
[0117] As shown in FIG. 13, a duty ratio characteristic 6060
corresponding to the motor current value required when the relative
rotational speed .DELTA.Nm is zero (.DELTA.Nm=0), namely, when the
electric motor 2060 is rotated at the same rotational speed as the
sprocket 2010 based on the rotational speed command value Nmref is
presented in a table in advance. DTY(ST) in. Equation 2 is set
based on the duty ratio characteristic 6060. Alternatively, DTY(ST)
in Equation 2 may be set by relatively increasing or decreasing the
value of the duty ratio corresponding to the relative rotational
speed .DELTA.Nm from the reference value based on the duty ratio
characteristic 6060. The rotational speed control, in which the
electric power supplied to the electric motor 2060 is controlled
using both the preset term and the feedback term in combination, is
executed. In this way, the electric-motor EDU 4100 causes the
rotational speed of the electric motor 2060 to match the rotational
speed command value Nmref, even if it changes, more promptly than
in a simple feedback control, namely, the rotational speed control
in which the electric power supplied to the electric motor 2060 is
controlled using only the feedback term DTY(FB) in Equation 2.
[0118] Next, the operations of the target phase restriction unit
4020 and the restriction range setting unit 4030 shown in FIG. 12
will be described in detail.
[0119] With the variable valve timing system according to the
embodiment of the invention, the intake valve phase when the engine
is started (the engine-start time phase) is set within the phase
region 2500, shown in FIG. 9, in which the speed reduction ratio is
high. Especially, in vehicles in which the engine intermittent
operation is automatically performed such as a vehicle provided
with an economy running system that automatically stops an engine
when the engine starts idling, and a hybrid vehicle that is able to
run using only a motor as a drive power source, preferably, the
start-time pressure reduction control for setting the start-time
phase to the most delayed phase is executed to reduce the vibration
when the engine is started.
[0120] The following description concerning the embodiment of the
invention will be provided on the assumption that the target phase
setting unit 4010 sets the target phase value IVref to the most
delayed phase (IVref=.theta.0) after an engine stop command is
issued, in order to facilitate the subsequent engine starting, as
shown in FIG. 14. After the engine stop command is issued, the
intake valve phase is controlled to change toward the most delayed
phase. Examples of an engine stop command include an engine stop
command issued in response to an operation performed by the driver,
typically, an operation to turn off an ignition switch, and an
engine stop command that is automatically produced by the engine
automatic stop control executed in, for example, a hybrid vehicle
or a vehicle provided with an economy running system.
[0121] Thus, the start-time pressure reduction control for reducing
the pressure in the combustion chamber is executed by the following
initial setting for the amount of air introduced into the
combustion chamber. According to the initial setting, the air once
taken in through the intake valve 1100 is returned to the intake
passage, the intake valve 1100 is closed, and then the compression
stroke is started. Because the pressure in the intake passage is
equal to the atmospheric pressure when the engine is being started,
the air is taken in the combustion chamber more efficiently when
the engine is being started than when the engine is continuously
operating, and the expansion of the air-fuel mixture caused by the
initial ignition tends to produce a great shock. However, according
to the embodiment of the invention, a torque produced by the
initial expansion of the air-fuel mixture that takes place in the
engine is reduced to suppress vibration of the engine, and
resistance to the cranking operation is reduced to start the engine
more smoothly.
[0122] The target phase setting unit 4010 sets the target phase
value IVref to the most delayed phase .phi.0 when start-up of the
engine is initiated (time t0). After start-up of the engine is
initiated, the target phase value IVref is set based on the engine
operating state, as described above. At this time, the target phase
value IVref may be gradually changed to avoid an abrupt change in
the intake valve phase, as shown in FIG. 14.
[0123] FIGS. 15 and 16 are flowcharts illustrating the manner in
which the target phase restriction unit 4020 and the restriction
range setting unit 4030 shown in FIG. 12 restrict the target phase
value. The routines for restricting the target phase value
according to the flowcharts in FIGS. 15 and 16 are executed when
the engine is operating, namely, when an engine stop command has
not been issued. The routines are realized by executing, for
example, the programs stored in advance in the ECU 4000 at
predetermined control cycles.
[0124] As shown in FIG. 15, in step S100, the ECU 4000 sets the
target phase value IVref based on the parameters indicating the
engine operating state. The process in step S100 corresponds to the
operation of the target phase setting unit 4010 shown in FIG.
12.
[0125] The ECU 4000 determines in step S120 whether the engine is
being started. The determination in step S120 may be made based on,
for example, an engine starting flag that is turned on in response
to issuance of an engine start command and turned off in response
to start of the self-operating of the engine.
[0126] When it is determined that the engine is being started
("YES" in step S120), the ECU 4000 restricts the target phase value
IVref to the phase region 2500 in which the speed reduction ratio
is high in step S140. Namely, when the target phase value IVref set
by the target phase setting unit 4010 in step S100 is more advanced
than the boundary value CA1 of the phase region 2500 shown in FIG.
9, the target phase value IVref is changed to CA1. The processes in
steps S120 and S140 correspond to the operation of the target phase
restriction unit 4020 in FIG. 12.
[0127] Thus, even when the engine is stopped in response to the
operation for turning off the ignition switch performed by the
driver while the engine is being started, the intake valve phase is
reliably maintained within the phase region 2500. As a result, it
is possible to prevent occurrence of an undesirable change in the
valve timing when the engine is being stopped.
[0128] On the other hand, when it is determined that starting of
the engine has been completed ("NO" in step S120), the ECU 4000
determines in step S200 whether the vehicle is not running based on
the vehicle speed detected by a vehicle speed sensor (not
shown).
[0129] When it is determined that the vehicle is not running ("YES"
in step S200), the ECU 4000 executes steps S220 and S240 to
restrict the target phase value IVref such that the target phase
value IVref is not set to a value more advanced than the phase
restriction value IVlmt. When the vehicle is not running even after
the engine is started, the engine is usually operating under
no-load conditions (i.e., the engine is idling). In a hybrid
vehicle, when the remaining battery charge is low, the engine is
sometimes operated under load conditions because the electric motor
is rotated to charge the battery. In these cases, the target phase
value IVref is set in step S100 with reference to the on-load
operation map 4012 and the no-load operation map 4014.
[0130] As shown in FIG. 17, the phase restriction value IVlmt is
set to a value that is more advanced than the boundary value CM of
the phase region 2500, in which the speed reduction ratio is high,
by the amount of .DELTA..theta.. Thus, the target phase value IVref
is restricted to the phase region 2500, in which the speed
reduction ratio is high, and a region 2550. The difference between
the boundary value CA1 of the phase region 2500 and a value in the
phase region 2550 is .DELTA..theta. at the maximum.
[0131] Thus, when the vehicle is not running, namely, when there is
a high possibility that an engine stop command is issued in
response to the operation performed by the driver to turn off the
ignition switch or an engine stop command is automatically issued
in a vehicle in which the engine intermittent operation is
performed such as a hybrid vehicle, the intake valve phase is
prevented from being apart by a large amount from the phase region
2500, in which the speed reduction ratio is high. Accordingly, when
an engine stop command is issued while the vehicle is not running,
the intake valve phase is reliably brought into the region 2500 by
the time the engine is stopped. Accordingly, it is possible to
prevent occurrence of an undesirable change in the valve timing
when the engine is being stopped.
[0132] As shown in FIG. 13, the phase restriction value IVlmt is
set such that .DELTA..theta. (FIG. 17) that defines the range, to
which the target phase value IVref used when the vehicle is not
running is restricted, is variable based on the engine temperature
(the coolant temperature). More specifically, based on the setting
characteristic indicated by a solid line 7000, the phase
restriction value IVlmt is set to .theta.a (IVlmt=.theta.a) when
the engine temperature (the coolant temperature) is lower than the
reference temperature Tj, while the phase restriction value IVlmt
is set to the most advanced phase and the target phase value IVref
is not restricted when the engine temperature is equal to or higher
than the reference temperature Tj.
[0133] Thus, even when the engine temperature is low, that is, when
it is difficult to achieve the required rate of change in the phase
due to an increase in the viscosity of the lubricating oil even if
the electric motor 2060 is rotated at a high speed, the target
phase value IVref is set to the appropriate range. When the target
phase value IVref is within the range, it is possible to bring the
intake valve phase into the region 2500 by executing the intake
valve phase control after an engine stop command is issued. The
reference temperature Tj and the phase .theta.a are empirically set
by determining the engine temperature at which the target phase
value IVref needs to be restricted and the rate of change in the
phase, which is achievable at the above-described engine
temperature.
[0134] Alternatively, based on the setting characteristics
indicated by dashed lines 7010 and 7020, the phase restriction
value IVlmt may be gradually delayed (.DELTA..theta. in FIG. 17 is
gradually decreased) as the engine temperature is gradually
decreased.
[0135] As shown in FIG. 16, in step S220, the ECU 4000 reads the
phase restriction value IVlmt in accordance with the engine
temperature with reference to, for example, the map, shown in FIG.
18, which indicates the setting characteristics. Namely, the
process in step S220 corresponds to the operation of the
restriction range setting unit 4030.
[0136] In addition, in step S240, the ECU 4000 restricts the target
phase value IVref to a value that is more delayed than the phase
restriction value IVlmt (to the region 2500 and the region 2550 in
FIG. 17). Namely, when the target phase value IVref set by the
target phase setting unit 4010 in step S100 is more advanced than
the phase restriction value IVlmt, the target phase value IVref is
changed to the phase restriction value IVlmt (IVref=IVlmt). The
process in step S240 corresponds to the operation of the target
phase restriction unit 4020.
[0137] On the other hand, when the vehicle is running ("NO" in step
S200), the ECU 4000 uses the target phase value IVref set in step
S100 as the target value used in the intake valve phase control,
without imposing any restrictions on the target phase value
IVref.
[0138] With the variable valve timing system according to the
embodiment of the invention described above, when the engine is
operating, especially, when there is a possibility that an engine
stop command is issued, the target value (the target phase value
IVref) used in the intake valve phase control is restricted in
consideration of the amount by which the phase can be changed by
the operation of the actuator from when an engine stop command is
issued until when the engine is stopped. Thus, the intake valve
phase is reliably within the region 2500, in which the speed
reduction ratio is high, when the engine is stopped. Accordingly,
it is possible to prevent occurrence of an undesirable change in
the valve timing when the engine is being stopped.
[0139] In the embodiment of the invention, the VVT mechanism 2000
(FIGS. 3 to 9) may be regarded as a "changing mechanism" according
to the invention, the target phase setting unit 4010 and step S100
(FIG. 15) may be regarded as a "target phase setting unit"
according to the invention, and the actuator operation amount
setting unit 6000 may be regarded as a "phase control unit"
according to the invention. The target phase restriction unit 4020
and steps S140 (FIG. 15) and S240 (FIG. 16) may be regarded as a
"target phase restriction unit" according to the invention, and the
restriction range setting unit 4030 and step S220 (FIG. 16) may be
regarded as a "variable restriction range setting unit".
[0140] The embodiment of the invention that has been disclosed in
the specification is to be considered in all respects as
illustrative and not restrictive. The technical scope of the
invention is defined by claims, and all changes which come within
the meaning and range of equivalency of the claims are therefore
intended to be embraced therein.
* * * * *